Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $180.79   8.743%   $196.5965   $196.60   $196.60   $196.60  
  Purchase #2 $167.53   7.475%   $180.0529   $180.05   $180.05   $180.10  
  Purchase #3 $81.62   7.299%   $87.5774   $87.58   $87.60   $87.60  
  Purchase #4 $167.89   4.229%   $174.9901   $174.99   $175.00   $175.00  
  Purchase #5 $47.76   6.506%   $50.8673   $50.87   $50.85   $50.90  
  Purchase #6 $188.80   9.117%   $206.0129   $206.01   $206.00   $206.00  
  Purchase #7 $30.88   10.437%   $34.1029   $34.10   $34.10   $34.10  
  7 purchase totals = $865.27       $930.2000   $930.20   $930.20   $930.30